Air navigation plotter



March 14, 1944. w, J, CTLETT, 5R` 2,343,883

AIR NAVIGATION PLOTTER Filed Sept. 5, 1942 mums nzlmwmonmslmcsnckz BY Y ATTO EY Patented Mar. 14, 1944 STATES ArtNr OFFICE (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. '757) 1 Claim.

This invention :relates to Ia plotting instrument for use in navigation and more particularly in aerial navigation, `and has certain advantages over the prior art which Will be disclosed presently.

It is the object of this invention to provide a device of the type mentioned that is iight, is of convenient size, can be inexpensively manufactured, and while being applicable to the solution of a large number of navigational problems, is

particularly applicable to the problem of plotting lines of position determined from observations of a celestial body.

With the above and other objects in view, the invention consists in the construction, combination and arrangement of parts as will be hereinafter more fully described.

The drawing shows the form of the invention that is at present preferred.

The subject device is preferably made of transparent Celluloid or the like and comprises a blade I having one longitudinal edge calibrated with a scale 3 representing nautical miles, in which the unit as shown is 20 miles Ito the inch, which is convenient for use in conjunction with usual aircraft plotting sheets :as these also have a scale of 1 degree of latitude equal to three inches. Scale 3 has its commencement on la transverse line a short distance from the lateral edge of rectangular blade I. Scale 3 is marked by equidistant transverse lines 5 :across the blade, and by numerals, every ten miles of representation. A portion of its length, near its commencement, also h'as markings every mile of representation. A series of equidistant longitudinal lines il, also spaced half an inch apart, form a grid for drawing parallel lines.

A quadrantal protractor f3 is formed by a projection of the material fof the rectangular blade from the edge 2 opposite scale 3 adjacent to the end where that scale commences. The center of fthe quadrant is located on the transverse line marking the commencement of scale 3, in line with the edge 2. At this center is a hole 'l v'through which4 a pencil point may be inserted.

The protractor has on it an angle scale 8, 90 degrees in length, extending from the edge 2 of the blade I. The 0 degree mark of scale 3 lies on the extension of the transverse line of the rectangular blade which marks the commencement of scale 3, which line also contains hole l. The 90 degree mark lies clockwise around the scale where the protract-or projection joins the edge 2 of the rectangular blade I. Scale 3 is marked at every degree and numbered at .ten degree intervals.

Under the numerals between 0" and 90 are placed those between 180 and 270, also running clockwise. 270 are placed those between 270 and 36D and below these those between and 180," both the latter series running counter-clockwise,

however, and engraved in reverse so as to be legible when the device is turned on the opposite side than that from the remainder of the scales are legible.

Broken lines are engraved connecting each series of numerals at the 10 degree positions of scale 8 with the hole l at .the center. The transverse lines 5 ladjacent to the protracltor are eX- tended thereon and crossed to form a continuation of the grid by a continuation of the series of longitudinal lines 4. Scale 9 is marked along the extension of the transverse line of the rectangular blade which marks the commencement' of scale 3, the scale commencing |at hole 'I and running towards the arc of the protracftonwith markings every mile of representation for a portion of its length and numerals every 10 miles of representation.

Practically all the methods of celo-navigation, by means of ,observations of celestial bodies, used in aerial navigation, and the great majority of the methods used in surface navigation, involve assuming a position on the earths surface in order to establish the third vertex of a spherical triangle 'on fthel celestial sphere having as its two other vertices the elevated celestial pole and the observed astronomical body. The third Vertex is the point on the celestial sphere directly above v the assumed position, the zenith. From'a latitude and longitude of the assumed position, the exact time of the observation, and the position on the celestial sphere of the observed body at this exact time, suicient dimensions of the astronomical triangle are kno-wn to permit its solution for the unknown part by means of a number of formulae, some having more iconvenience than others. The unknown parts desired are those which determine the altitude, or

Under the numerals to' i be the same.

line which has a `direction at right angles to the4 azimuth of the observed body. Thus yshouldjtlre computed altitude using the assumed position z equal the corrected observed altitude'the naviga-v tor will know he is on aline of position passing through the assumed position and at right angles to the azimuth of the observed body. From a position a few miles from such a line the corrected observed altitude would differ from the altitude computed by using an assumed position by the 'same number of minutes of arcas the dife ference in nautical miles'between the actual po- Y sition and this line. Ifthe Vcorrected, observed altitude is greater than the computed altitude the actual position isl towards the observed body from s the assumed position, and if less it is away.

Thus, should the corrected 4observed altitude differ from the Vcomputed altitude the navigator may plot his line offposition by measuring a dis- 1 tance towards or away from the assumed position, in the direction'of the azimuth of the observed body, equal tofthe difference between the observed and computed altitudes, and drawing his lineof position through the-point thus ob tained at right angles to the azimuth. Itis rto facilitate this plotting that the4 present inven-v tion is particularly adapted.

Having determined the azimuth and the differencebetween the computedl and the corrected observed altitudes, or the altitude intercept, with this invention the navigator places theY plotter on they plottingfsheet or chart so that scale 8 willV represent the quadrant in which the azimuth is located. If the azimuth is greater than 270V de-l grecs' or less than 90 degrees this will be with the 0 degrees mark of scale 8 towards th'enortherly direction as 44represented onlthe plotting sheet orchart. `If the azimuth isbetween 90 degrees and` 270 degrees, this `will be with they 180 degrees mark merals ofthe appropriate quadrant are legible,V

of scale4 towards the southerly direction. The face of the plotter must b'e up on which the nurather than reversed. The navigator then places hole 1 over the assumed Ypositionland turns the instrument sothe longitudinal ilines 4 of the grid A are parallel to the latitude, and the transverse lines5 are parallel to the longitude lines of the chart or plottingsheet, using his pencil point placed through hole 'I tovfacilitate this positioning. A mark placed on theV lplotting sheet or chart opposite the azimuth as indicated on scale V8` servesto establish the line of bearing of the celestial body. :The plotter/is now placed with the edge of blade I at the initial point of scale 3 on fthe assumed position, the edge lying in the line o-f bearing of the observed body just established, and a distance equal to the altitude intercept i's marked ofi on the chart or plotting sheet'. When a chart or universal plotting sheet with scale of 1 degree latitude equals 3 inches is used scale 3 can be used directly; otherwise it will be necessary to utilize the chart scale to convert the altitude intercept to distance on the plotting sheet or chart. By now placing the plotter so hole 1 is over the foot of the altitude intercept and turning the plotter so one end of scale 8 lies in the line of bearing of the observed body, a mark on the plotting sheet or chart opposite the Aother end of scale 8 will determine the line of position through the altitude intercept which can be, drawn by placing the edge of blade I on the line just determined.

It is thus apparent that with the use of this invention lines of position may be rapidly and accurately plotted in a more convenient manner than by the use of a drafting machine, parallel rulers, plotter requiring clamping and unclamping of a movable arm, determination of a reciprocal azimuths as would b'e necessary almost onefourth of the time when using the device of U. S. Ratent 1,985,907, or other devices known to the prior art.

It will be understood that the above description and accompanying drawing comprehend only the general and preferred embodiment of my invention and that various changes in construction, proportion and arrangement of parts may be made within the scope of the appended claim without sacrificing any of the advantages of my invention.

' The invention described herein may be manu-l factured and used by or for the Government of the United States of America for'governmental purposes Without the payment of any royalties thereon or therefor. Y

Y I claim:

A transparent integral navigational plotting instrument comprising a rectangular rule portion substantiallylZ inches long having a quadricircular portion with one radial edge along a long edge of the rectangular portion, the other radial edge beingflush with the end portion thereof and a narrow rectangular strip portion along .this end and the said other radial edge, a pencil point perforation being made at the juncture of the three portions, the instrument having rectangular grid lines at half inch intervals, forming scales longitudinally and transversely of the instrument originating at the lines intersecting at the perforation, the grid lines being marked numerically` with 10 unit intervals in the numerals, the first few spaces between the grid lines along the outer edges of .the grid markings being subdivided into 10 divisions in each space, the arcuate edge of the quadricir-cular portion being divided into a one degree scale, every 10 degree division being connected by a light radial line with the perforation,

and the deg-ree scale being marked at the 10 degree intervals by four sets of numerals, two covering the 90 degree ran-ges from 0 to 90 and 180 to 270 and running in a clockwise direction, the other two covering the 90 to 180 and 270 to 360 ranges and running in a counter-clockwise di-` Y 'reci'.ion, the latter two sets being engraved in reverse soY as to be legible from the opposite side of the instrument.

' WILLIAM J. CATLETT, Jn. 

